The present invention relates to a compressor, and more specifically to a compressor used in a reversible refrigeration cycle, such as an air conditioning system of a heat-pump type, which can shift its operation between cooling and heating modes.
In general, reversible refrigeration cycles, such as air conditioning systems of a heat-pump type, which can be shifted between cooling and heating operations, comprise a compressor, a four-way valve, an outdoor heat exchanger, an expansion valve as a pressure reducing device, and an indoor heat exchanger. These components are connected by means of refrigerant pipes to form a closed cycle. Those compressors conventionally used in small-capacity air conditioners for home use, for example, are rotary compressors which are small-sized and high in rotating efficiency.
As the compressor is rotated, a refrigerant is compressed and discharged into the refrigerant pipes. In a cooling mode, the refrigerant delivered from the compressor is returned thereto successively through the four-way valve, outdoor heat exchanger, expansion valve, indoor heat exchanger, and again the four-way valve. In a heating mode, the four-way valve is shifted so that the refrigerant discharged from the compressor is returned thereto via the four-way valve, indoor heat exchanger, expansion valve, outdoor heat exchanger, and again the four-way valve.
In both cooling and heating modes, the rotating direction of the compressor is fixed, so that the refrigerant is discharged always in a predetermined direction. The operation mode is switched by shifting the direction of the refrigerant flow in the four-way valve. Generally, the four-way valve comprises a valve body, a pilot valve in the body, and a solenoid for operating the pilot valve. Thus complicated in construction, it is very liable to malfunction or is low in reliability, and costs high. Since the valve body is connected with the respective ends of four refrigerant pipes, a wide space is required for the pipe arrangement, and the pipe connection is troublesome. The switching of the four-way valve requires a relatively large driving force, and therefore use of a large-sized solenoid. In this case, power consumption increases, so that the operating cost of the air conditioning system also increases. During the switching operation, moreover, the valve mechanism and refrigerant produce noises.
Thus, the four-way valve is expected to be replaced by some other means of switching the flowing direction of the refrigerant which is simpler in construction, higher in reliability, and more attractive in cost.